Identification of sumoylated proteins in the silkworm Bombyx mori.

School of Biotechnology, Jiangsu University of Science and Technology, Zhenjiang 212018, China. xudongt@aliyun.com.

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School of Biotechnology, Jiangsu University of Science and Technology, Zhenjiang 212018, China. jtv215@126.com.

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School of Biotechnology, Jiangsu University of Science and Technology, Zhenjiang 212018, China. bfhao@just.edu.cn.

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School of Biotechnology, Jiangsu University of Science and Technology, Zhenjiang 212018, China. zf200537@163.com.

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School of Biotechnology, Jiangsu University of Science and Technology, Zhenjiang 212018, China. shengyanxiao1989@126.com.

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School of Biotechnology, Jiangsu University of Science and Technology, Zhenjiang 212018, China. zjcysxl@163.com.

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School of Biotechnology, Jiangsu University of Science and Technology, Zhenjiang 212018, China. szysri@163.com.

Abstract

Small ubiquitin-like modifier (SUMO) modification (SUMOylation) is an important and widely used reversible modification system in eukaryotic cells. It regulates various cell processes, including protein targeting, transcriptional regulation, signal transduction, and cell division. To understand its role in the model lepidoptera insect Bombyx mori, a recombinant baculovirus was constructed to express an enhanced green fluorescent protein (eGFP)-SUMO fusion protein along with ubiquitin carrier protein 9 of Bombyx mori (BmUBC9). SUMOylation substrates from Bombyx mori cells infected with this baculovirus were isolated by immunoprecipitation and identified by LC-ESI-MS/MS. A total of 68 candidate SUMOylated proteins were identified, of which 59 proteins were functionally categorized to gene ontology (GO) terms. Analysis of kyoto encyclopedia of genes and genomes (KEGG) pathways showed that 46 of the identified proteins were involved in 76 pathways that mainly play a role in metabolism, spliceosome and ribosome functions, and in RNA transport. Furthermore, SUMOylation of four candidates (polyubiquitin-C-like isoform X1, 3-hydroxyacyl-CoA dehydrogenase, cyclin-related protein FAM58A-like and GTP-binding nuclear protein Ran) were verified by co-immunoprecipitation in Drosophila schneide 2 cells. In addition, 74% of the identified proteins were predicted to have at least one SUMOylation site. The data presented here shed light on the crucial process of protein sumoylation in Bombyx mori.

The subcellular localization of small ubiquitin-like modifier of Bombyx mori (BmSUMO) in BmN cells. The cells were treated with anti-BmSUMO antibody, and the fluorescent signal was developed by incubating the cells with Protein G fused with enhanced green fluorescent protein. As a control, pre-immune serum was used as the primary antibody. The nuclei were stained with 4',6-diamidino-2-phenylindol (DAPI). The samples were viewed using a confocal laser fluorescence microscope. (Scale bars = 20 and 5 µm respectively).

Gene ontology (GO) categories of SUMO-conjugated proteins. Proteins were classified into Biol. process, cellular component, and molecular function categories by Web Gene Ontology Annotation Plot (WEGO), according to the GO hierarchy. The number of proteins mapped to the GO terms is shown on the right axis. The left axis shows the proportion of total proteins mapped to the GO terms.